1. Field of the Invention
The present invention relates to a method to provide temporary fixation of orthopedic devices, in particular intramedullary rods, other fracture fixation devices, and prostheses, that provides a substitute for conventional methods for fixation at both the distal and proximal end of the device.
2. Background of the Art
Interlocking intramedullary rod nailing requires fixation of the distal and proximal portions of an intramedullary rod to a bone. Typically, the canal of the bone is drilled from a proximal to a distal end of the bone and an intramedullary rod is inserted. Transfixion screws are then placed through holes in the intramedullary rod. To insert the screws, holes are drilled through the bone at an angle of between about 30 and 90 degrees to the rod, and screws are inserted through the holes to lock the intramedullary rod in place.
As will be appreciated, since the rod is buried in the intramedullary space of the bone, aiming devices or jigs are necessary in order to accurately drill the holes through the bone to match up with the holes of the intramedullary rod. This technique is relatively straightforward near the proximal end of the intramedullary rod (near its point of insertion). In this region, a relatively short-armed aiming device can be attached to the intramedullary rod for reference. Thereafter, a drill can be passed through the bone and a proximal hole.
However, in the distal region, accuracy is affected due to the distance between the reference point (the proximal end of the rod) and the point where the holes must be drilled. Freehand drilling while watching a fluoroscopic image intensifier to accomplish distal targeting is one solution to this problem. However, this technique is difficult to use and adds the additional risk of exposing the patient and surgical team to radiation. E.g., Muller et al. J. Bone & Joint Surgery (hereinafter abbreviated "JBJS") 65A:1-4 (1983); Levin et al. JBJS 62B:227-229 (1987); Rao et al. Clin. Ortho. Rel. Res., 238:245-248 (1989); Gachino et al. JBJS, 69A:761-766 (1987).
The Brooker-Wills rod attempts to circumvent the problem presented by the difficulties encountered in fixing the distal end of intramedullary rods. This rod functions through use of an internal mechanism in the rod that allows placement and deployment of expandable fins from the distal end of the rod. While easier to use, the rod is fixed less rigidly, rendering the intramedullary rod less effective against axial and torsional loads. E.g., Johnson et al. Clin. Ortho. Rel. Res. 206:151 (1986); Kyle et al. Clin. Ortho. Rel. Res. 267:169-173 (1991); Bankston et al. CITE! (1992).
Despite these problems, all of the interlocking nail techniques share in common an enhanced ability to control the axial and torsional forces that are often encountered where such interlocking is not used. Shortening and angulation of the fractured bone are prevented, resulting in a superior ability to restore the normal anatomy of the patient. Further, because of its success, the use of interlocking screws with intramedullary rods has gained favor in the treatment of comminuted and unstable fractures as well as other fractures located proximal or distal to the mid-diaphysis where good nail fixation has been difficult to achieve with conventional rods.
The clinical results of interlocking intramedullary rods with screws have been impressive. E.g., Johnson et al. JBJS 66A: 1222 (1984); Kempf et al. JBJS 67A: 709 (1985); Browner et al. Contemp. Ortho. 8:17-25 (1984); Thoresen et al. JBJS 67A:1313 (1985). In particular, comminuted fractures of the distal and proximal one-third of the femur and tibia that previously could not be managed by closed intramedullary nails are now candidates for interlocking rod fixation. The rapid functional recovery and lower morbidity associated with this technology will likely further the indications for, and use of, this technique.
Complications with interlocking nails have been noted, however. These include difficulty of screw placement, as discussed above, and bending, fracturing, and/or loosening of the nail or other implant. Shifflett et al. Complications in Ortho. 116:.sub.13 (1987); Bucholtz et al. JBJS 69A:1391 (1987). There is also the concern of increased operative time and radiation exposure with the interlocking process. These particular complications are specifically related to the design and use of the interlocking rod.
Another avenue that has been explored is the permanent fixation of intramedullary rods as well as protheses in the intramedullary space within bones through the use of certain synthetic polymer cements. In particular, the use of methyl acrylate, polymethacrylate, or polymethylmethacrylate (PMMA) styrene copolymers has been suggested. E.g., U.S. Pat. No. 4,065,817 to Branemark, et al.; U.S. Pat. No. 4,494,535 to Haig; and U.S. Pat. No. 4,635,489 to Tronzo.
Of the patents mentioned above, U.S. Pat. No. 4,494,535 to Haig and U.S. Pat. No. 4,635,489 to Tronzo both disclose the permanent fixation of a hip nail with an acrylic cement. Also, a system has been proposed that is useful for prevention of fractures and augmentation of the osteopenic skeleton. The system involves the insertion of an intramedullary rod in the femur and the injection of acrylate polymer cement to permanently fix the rod within the femur. See U.S. Pat. No. 4,653,487. However, this latter system is designed specifically for preventing an intramedullary rod from telescoping through a weakened and diseased bone; i.e., augmentation, not for the repair of a fracture or for the fixation of a prosthesis anchor.
Synthetic polymer cements cure through exothermic reactions, thereby producing elevated temperatures in the surrounding tissues while undergoing polymerization. For example, PMMA cements typically react and release heat at up to 50.degree.-70.degree. C. This may lead to tissue destruction around the area where the cement is applied causing occlusion of nutrient arteries in the bone. Similarly, certain of the cements are toxic to surrounding tissues upon introduction and may also lead to cell death. If no cell death occurs, the cements may lead to local inflammation. Once polymerized, the cements remain in the bone permanently.
To combat these problems, several partially or completely resorbable bone cements have been proposed. E.g., U.S. Pat. No. 4,296,209 to Tomic (partially resorbable effervescent composition based on polymethylmethacrylate, calcium carbonate, and disodium hydrophosphate); U.S. Pat. No. 5,019,379 to Domb et al. (resorbable unsaturated polyanhydride compositions); U.S. Pat. Nos. 4,365,357 and 4,373,217 to Draenert (partially resorbable mesh for allowing ingrowth into nonresorbable PMMA-type cements and partially resorbable PMMA-type cements with tricalcium phosphate, respectively); and U.S. Pat. Nos. 4,880,610, 5,047,031, 5,053,212, and 5,129,905 to Constantz (resorbable hydroxyapatite compositions).
A need therefore remains in the orthopedic fixation art for a method to provide fixation of devices within bones that alleviate the problems of difficulty of interlocking of intramedullary structures, bone ingrowth incompatibilities with conventional cements, and attainment of the necessary strength and rigidity of the implant, and ultimate removal of the cement by natural biologic processes.